How does draw strength affect accuracy?

Posted by ZDP-189, in Technical 08 August 2010 · 237 views

I've known for a while that the heavier I have to pull, the less accurate and consistent my shots are. I've been looking for ways to describe or quantify that, because I want to establish my optimum draw strength for accuracy. By using heavier bands and heavier ammo I should shoot flatter and straighter, but after a certain point, inaccuracy starts to creep in.

My current approach is to use a laser attached to the frame.

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I cut a precise groove in the centre of the base, aligned perpendicular to the plane of the forks. Actually, this accuracy is not necessary for the test.

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The groove accepts a sight rail which is screwed on. The laser sight is fixed to the rail.

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It is shown with a pressure switch, but for the tests I used a second end cap that has a constant-on switch.

Note that this device is not for aiming or even for live firing. Slingshots are not aimed like that. It is the relative position of the fork and pouch hand that aims the shot, not the way the fork is pointing. Instead what this device does is reveal the degree to which the fork is wobbling.

ZDP-189
Aug 08 2010 12:13 PM

I shot 1 second timed exposures to show the spread (area), track (line) and time on position (brightness). The range was approximately 10 yards/ 10m and the rings are 1" wide, 2" wide and 3" wide.

Control: No Load

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The control is my baseline. You can see it all stays in the 3" ring and moves slowly.

Fork Held in Two Hands

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This simply illustrates that steadying the fork achieves less spread and slower movement.

7lbs Draw Weight

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With a little weight, I can see more movement, but it's still under control.

11lbs Draw Weight

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There is no significant degradation at 11 lbs.

14lbs Draw Weight

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At 14 lbs, there is more significant wobble. I'd need heavier bands to test a stronger draw.

Some thoughts:

The device can be used to train myself to hold the slingshot steady.
I was holding the slingshot vertically in a finger high position. I need to test a hammer grip and holding the slingshot sideways. I also need to test different slingshots.
I was expecting vertical movement, as that's the direction of twisting when I pull. I got a lot of sideways movement. That means one band will be under more tension than the other and increases the chance of fork hits, spin and side-to-side inaccuracy.
I had some bias to the right at 14lbs. That explains why I have had two fork hits on this slingshot. Tonight's hit was in exactly the same spot as last time and this time I got my finger in the way, actually leaving some skin on the slingshot. I will be selling this slingshot on later after these tests. The slingshot is a fine shooter, but I am too used to flip style shooters.

whipcrackdeadbunny
Aug 09 2010 06:35 AM

Excellent! Once again.

NightKnight
Aug 09 2010 08:08 AM

Wow! That is a great idea, and a great post!!

ZDP-189
Aug 10 2010 01:49 AM

With respect, I think I prefer my heart beating.

If you refer to the reference picture called Fork Held in Two Hands, I think some of that wandering may be due to heart beat. Some of that I can accept, because it's a 1 second exposure and in shooting, I can time the shot between beats. The purpose of the testing is to keep it looking more like the 7-11 lb pictures and no worse than the 14lb picture.

NightKnight
Aug 12 2010 04:28 PM

You know, this could explain why I am more acurate with the Saunders Wrist-Rocket Pro. The resistance is only against major muscles.